This protocol is attempting to reduce the toxicity associated with IL-2 therapy without interfering with its anti-tumor activity. It combines the standard Interleukin-2 regimen, as approved by the FDA, with the experimental agent, CT1501R , a metabolite of pentoxifylline, the blood levels of which has been shown to correlate with improved tolerance to IL-2 therapy. The dose of CT-1501R to be used in this study was determined in a phase I study combining it with IL-2 to produce steady state blood levels.